Help please... canti boss issue driving me insane

[finbar]

I've spent way too much time and money trying to sort what should be a really simple part to fit.

My frame has replaceable M10 canti studs front and rear. I had to get new sets because the old ones were knackered - so far, so easy.

But every pair I can find has a larger-diameter part at the base that is preventing my cantis from reaching the bottom of the boss. In turn, this means the spring pin barely engages with the hole in the frame and pops out at the slightest rotation of the brake. The picture hopefully illustrates what I'm on about.

What's going on? Looking at an old steel frame I have, the canti studs don't have the larger diameter part (and lo and behold, brakes fit fine). I've tried Shimano R550 and Tektro CR710 cantis, same issue with both.

Thanks for any advice. I hope that makes sense.

 

[Frankenorange]

Those bosses with a shoulder are meant for frames that have a counterbore in whatever is mounted on the forks or stays. The shoulder goes into that counterbore if you get my drift. Maybe removing the shoulder using a file/grinder/sanding wheel will allow it to work.

 

[pwebb]

hmm, I have seen this before when using m10 studs from amazon/ebay on modern forks ( not vintage frames/forks) I am pretty sure that those older shimano cantis are intended to use an m8 stud not m10 and the stopper pin of the spring wont reach by 2mm - you need some cantis that were either designed for either m8 or m10 studs or have external springs - like the shimano CX50 and cx70 ( aka shimano 105) and similar more modern canti brakes designed for cx bikes. alternatively brakes that dont use the stopper pins at all - like Paul minimotos and neo retro that have their own pivots and are self tensioning. Either that or fit v brakes I reckon. I am surprised at the Tekro CR710 but that design still has the recessed springs - I think the key with 10mm v brake bosses is having the external style springs rather than self contained recessed ones. when I look at the CX50s mounted on a 10mm post ( e.g. surly frame and forks) there is a big gap between the brake arm and the canti boss but fortunately the stopper pins on the springs reach aok. I think its all about the design of the canti whether you have this issue or not - I will try to take some pics of brakes that circumvent this issue

 

[pwebb]

here are some pics showing the gap in question on various frames and forks:

shimano CX50 on surly fork with 10mm studs -





Paul neo retro canti on modern alu fork with 10mm studs from amazon (stopper pin not used, spring is on front of brake arm not the back)



Paul minimoto ( essentially a v brake but again doesnt use the stopper pin at all) - here its is on a surly fork -


shimano CX50 on a surly cross check frame with 10mm stud - spring just reaches ok -

i hope you find some cantis that work for you - else you may have to resort to grinding the shoulders off the base of the studs - or finding someone with a lathe to do the same

 

[2manyoranges]

can you post a photo of the boss mounts in the frame? It may be that you do have a counterbore but that the threaded section is too long on the replacement bosses. The threaded section comes in different lengths on different bosses.

 

[finbar]

Thanks all, this is very helpful - but also confirming what I feared.

I'll post photos tomorrow, but the frame is (a) definitely not counterbored; and (b) the threaded section of the posts is bottomed out.

I have a grinding wheel so I think my first step will be to try removing the lip. If that fails, second will be hunting down some CX50s, I rather like those anyway. Wish I'd got them in the first place instead of the Tektros though :-( .

 

[2manyoranges]

hmmm.....

 

[2manyoranges]

Note these have very short threads

https://www.ebay.co.uk/itm/29650246...OKV17T6gWSgStqTYdiRbhdXMQ=|tkp:Bk9SR467zKiMZg

 

[Frankenorange]

hmmm.....


View attachment 986269

There is a fourth type which typically is what you find on an aluminium frame and that is a welded on lump with 3 holes and the counterbore for a shouldered boss

 

[ishaw]

I've got a load of frame bosses kicking around either new or from where I've replaced steel with ti. I can have a look to see if any don't have the shoulder.